1. Field of the Invention
The present invention relates to a machining liquid filtration device in an electric discharge machine such as a wire-cut electric discharge machine, and relates particularly to a filtration filter of the electric discharge machine, which filters sludge in a machining liquid.
2. Description of the Related Art
In an electric discharge machine such as a wire-cut electric discharge machine, in order to remove sludge such as minute metal scraps of an object to be machined having been discharged during machining and existing in a machining liquid, there has been used a filtration filter formed by folding a filter medium, such as synthetic fiber and cellulose, and by packing the filter medium into a cylindrical metal container or a cylindrical resin container. Here, a combination of a filter medium and a filter outer cylinder container outside the filter medium forms is called “filtration filter”.
JP 2005-161279 A discloses a filter which has a filter outer cylinder formed of a punching metal and a large number of fluid passage holes formed in a cylindrical outer wall surface of the filter outer cylinder.
JP 2000-77749 A discloses suppression of an increase in the ion concentration of cooling water due to contact with air while keeping the pressure in a tank constant, maintaining a high resistance value of the cooling water, and extending a life of an ion exchanger.
In JP 2007-276021 A, in order to extend a life of an ion-exchange resin, there is disclosed a device which is provided with a filter holding tank for immersing a filter and is characterized in a liquid discharge unit which discharges a liquid from the filter holding tank.
JP 7-60555 A discloses a device which submerges a filter body in a container separate from the filter body to maintain uniformity of progression of filter clogging, and reduces the flow rate per unit area to extend a filter life.
In general, as disclosed in JP 2005-161279 A, the fluid passage holes opened in the filter outer cylinder container are uniformly opened in the entire side surface of the filter outer cylinder container. Thus, a machining liquid passing through a filter medium unevenly flows through the filter medium due to influence of gravity and clogging of the filter medium. Namely, the clogging progresses from a bottom portion of a filter.
Thus, since the clogging of the filter medium nonuniformly progresses, the flow rate per unit area to the filter medium increases. Since the square of the flow rate and a pressure applied to the filter medium are proportional to each other, a filter pressure easily rises, so that the life of the filter medium is shortened.
In JP 2000-77749 A, in order to extend a life of an ion-exchange resin, there is proposed a structure in which a filter outer cylinder container storing a filter medium is submerged in a clean-water tank. In JP 2007-276021 A and JP 7-60555A, in order to extend the life of the ion-exchange resin or the filter, there is proposed a method of immersing the filter outer cylinder container storing a filter medium in a container separate from the clean-water tank.
However, since the separate container is required to be provided in order to submerge the filter outer cylinder container storing the filter medium, an extra installation space for the separate container and cost are required, and thus the method is not preferable.
In JP 7-60555 A requiring the container separate from the filter outer cylinder container, since it takes time from immersion of the machining liquid, having passed through the filter, in the separate container to overflow of the machining liquid to the outside of the separate container, the time is required until the machining liquid begins to be stored in the clean-water tank. Thus, an alarm may occur due to shortage of the machining liquid in the clean-water tank, or a pump in the clean-water tank may run idled, resulting in a failure. When the separate container is used, it is difficult to insert or remove the filter in or from the separate container while the filter is adhered firmly to the container.